1. Field of the Invention
This invention relates to a photographic camera, and more particularly to a camera having a piezo-electric actuating element which is distorted in response to a voltage applied thereto.
2. Description of the Prior Art
Conventionally, various proposals have been made to a camera of the type wherein a piezo-electric actuating element as described above which is also known as a bimorph is employed for actuation of a photographing lens for focusing or of a shutter. Typical ones of such cameras are disclosed, for example, in Japanese Patent laid-open No. 60-144726 and in Japanese Patent Laid-open No. 59-204014.
In order to apply a stabilized high voltage across such a piezo-electric actuating element as is used for actuation of a lens or a shutter to drive the piezo-electric actuating element in stability, it may be advisable to once accumulate in a capacitor a charge of a voltage necessary to drive the piezo-electric actuating element in stability and then supply the charge thus accumulated to the piezo-electric actuating element upon actuation of the same for photographing. Further, as it is considered that subsequent photographing may be done in a moment, it is necessary that, when a subsequent photographing operation is started, the capacitor is already charged up to a voltage sufficient to drive the piezo-electric actuating element in stability because actuation of a shutter or a lens by the piezo-electric actuating element is essentially required for such photographing.
In other words, if a subsequent photographing operation is stated before the capacitor is charged up to a voltage sufficient to drive the piezo-electric actuating element in stability, the lens or shutter which is connected to be actuated by the piezo-electric actuating element will not operate regularly. Accordingly, there is the possibility that photographing in error such as photographing with out of focus condition or with improper exposure may be done.
Meanwhile, a main capacitor of a flash device which is provided to supply energy for emission of light to a xenon tube of a flash for flash photographing makes a high load to a power source. Accordingly, if the capacitor for the piezo-electric actuating element is charged in simultaneous relationship with the main capacitor of a flash device, much time is required to completely charge up both the capacitors, which will disable subsequent photographing to be performed in a moment. Accordingly, such simultaneous charging of both the capacitors is not preferable.
Further, such a piezo-electric actuating element presents a following problem due to its hysteresis characteristic which is well known in the art. In particular, if it is assumed, for example, that a voltage of 0 volts is applied across a piezo-electric actuating element at in initial position and that a voltage of 200 volts is first applied across the piezo-electric actuating element in order to actuate a shutter and then the voltage of 0 volts is applied again across the piezo-electric actuating element after operation of the shutter, the piezo-electric actuating element will not return to its initial position due to its hysteresis characteristic. Accordingly, if the voltage application to the piezo-electric actuating element is controlled upon subsequent operation of the shutter on the assumption that the piezo-electric actuating element has been returned to its initial position, operation in error will occur.